Visit to IHEP 16-27 September 2015: recommendations for CEPC M. Koratzinos IHEP, Beijing, 25/9/2015

Topics During my stay I had the opportunity to work on the following topics: Partial double ring (bowtie design) Booster ring MDI I participated on the following meetings: IAC meeting 16-17/9/2015 (observer) MDI meeting 22/9/2015 (presentation) Ad hoc meetings, Jie Gao’s office: 21-22-24/9 This meeting

MDI It is essential to leave more space for the long straight section close to the experiments. Recommendation: increase the length of the long straight section to 3kms (1.5kms×2). If the IR design does not need all this space, it can be given back Constrain the last dipoles to emit less than 100KeV photons Do not pay attention at beam separation for the moment. Reduce the magnetic field of the experimental solenoid to 2T Increase L* from 1.5 to 2m, otherwise there is not enough space for all magnetic elements needed (anti-solenoid, compensating solenoid), plus luminometer

Partial double ring I call it ‘bowtie’ design Use standard LEP separators (this is already done) and consider a defocusing quadrupole to save space. Close the ring, introducing a 15mrad×2 crossing angle at the experiment. Introduce a crab waist scheme. The CW scheme needs as small emittances as possible to operate efficiently. Reduce the horizontal emittance by choosing a smaller FODO length of 38m and consider 90 degree optics (like FCC-ee)

Booster ring Current booster ring with 6GeV injection will have problems Already suggested (work under way) to make the booster ring as a whole a mega-wiggler Like this, the minimum magnetic field can be 6-7 times larger than in the pre-CDR case. Possible problems: particles will be off their central orbits by ~1cm; quads will be crossed off-center; the power supply needs to cross the zero current regime.